The present invention relates to a method and apparatus to mix polymeric compounds, and more particularly to a method and apparatus to mix elastomers such as rubber with agglomerates of compounds such as carbon black whereby the agglomerates are broken up and dispersed throughout the elastomer.
Mixing apparatus and various types of treatment apparatus to treat macro molecular substances are known; one such apparatus utilizes a pair of essentially cylindrical compression cylinders which are separated by a nozzle block through which nozzle-shaped ducts pass. The treatment substance is included in the cylinders and pushed back and forth, through the apertures, to mix substances therein, or to treat substances by wall contact with the nozzle block.
In the specification and claims, the term xe2x80x9ctreatmentxe2x80x9d should be understood to mean a wide variety of operations and processes, and not only mixing. For example, other treatment processes may be plasticising, inter-mixing, adding and mixing, homogenizing, dispersing, separately or combined with further treatment operations such as addition of heat; removal of heat; extrusion through nozzles or constrictions; evaporation; vacuum treatment; or other treatment steps such as, for example, breakdown of macro molecular substances under increased pressure, for example gas pressure, linking, cross linking, or polymerization of substances and other process and treatment steps.
Various types of apparatus have been proposed in order to treat compositions of matter in accordance with the one or the other desired treatment operation. Most such apparatus have specific advantages, but also specific disadvantages, so that various treatment steps can be carried out only partially, or by use of expensive or uneconomical processes.
One type of well-known treatment apparatus is the so-called Banbury mill. A pair of steel rollers, the temperature of which can be controlled, is located to form a slot or nip therebetween and substances to be mixed are pulled or drawn through the slit between the rollers. Depending on the width of the slit, and the difference in circumferential speed of the rollers, the substances being pulled through the slit are stretched, sheared, or mixed more or less. Proper use of the machine requires skilled and attentive operators. Additionally, the process is difficult to control and output which is not properly mixed is frequent; the output must, therefore, be constantly tested. In spite of these disadvantages, and in spite of the high labor cost for a unit of mixed output, the open mixing roller-type mill apparatus is widely used, primarily due to its versatility and adaptability to various substances.
Single-chamber enclosed mixers, of the Banbury or Werner and Pfeiderer type use a closed chamber, in which the substance to be mixed is included. A pair of shafts with eccentrically located projections or lands pass through the chamber, so that the goods to be mixed are placed under shear stress. This apparatus permits high shearing speed to occur only at localized regions and no assurance is given that all particles are subjected to passage through a zone of high shearing speeds during a plurality of times, as is required for homogenizing. Additionally, the substances to be mixed experience a temperature rise so that high shearing stresses cannot be obtained, necessary for dispersions, due to the decrease of viscosity. Cooling the chamber itself usually is not sufficient to remove generated heat, since particularly macro molecular substances have a low heat conductivity. It is thus necessary to continuously peel off substance to be treated from the wall of the chamber. This peeling off of substance is carried out frequently only insufficiently. The chamber itself is subject to wear and tear and can be repaired, or serviced only in substantial intervals. In the meanwhile, the distance between a peeling apparatus and the wall of the chamber itself may become excessive. Increasing the temperature during treatment frequently is undesirable if components of the substance are heat sensitive; chemical reactions may result which may require that substance, which is not yet completely treated, must be removed from the enclosed mixer and immediately cooled, for example, by intermediate cooling on a cooling mill or roller. The mixing chamber should be completely full. Treatment in which various elements or components should be treated in sequential steps is difficult to be carried out since the quantities to be mixed have to be matched to the required mixing quantities, at any time during the steps, which interferes with economical operation of the system and the treatment method.
In U.S. Pat. No. 3,860,218 (""218) there is disclosed, for example, xe2x80x9ca nozzle block, formed with at least one and preferably a plurality of parallel ducts is clamped between a pair of pressure cylinders, between which substances are pushed from one side of the block, through the block to the other. The cross section of the connecting duct, or ducts is selected, in accordance with the present invention, to be non-circular.
The nozzle block can readily be removed from its clamped position between the pressure cylinders and easily replaced. The connecting nozzles or ducts, between the pressure cylinders, can thus be designed to fit the desired process, and can be easily formed with necessary connections for cooling, heating, for the addition of test or sensing elements, and can be placed to be externally freely accessible.xe2x80x9d
Further there is disclosed, for example, in the ""218 patent, xe2x80x9can apparatus to treat compositions of matter: and more particularly to mix macro molecular substances.xe2x80x9d The nozzle blocks disclosed in the ""218 patent are xe2x80x9cparticularly designed to plasticise raw rubber.xe2x80x9d However, there is no teaching or suggestion in the ""218 patent of mixing an elastomer with agglomerates of compounds whereby the agglomerates are broken up and dispersed through the elastomer.
According to the present invention, there is disclosed a method for mixing a polymer with an agglomerates of one or more compounds which comprises the steps of: disposing an amount of the polymer and an amount of the agglomerates of the one or more compounds into one of a pair of opposed pressure cylinders; providing a nozzle block located between the opposed pressure cylinders and being formed with at least one duct of non-circular cross section establishing communication between the cylinders; moving the pistons to force the polymer with the one or more agglomerates of the compound from the one of a pair of opposed pressure cylinders into the other opposed cylinder and back so that the agglomerates of the compound are broken up and dispersed throughout the polymer; and removing the polymer with the broken up agglomerates dispersed therethrough from one of the pair of opposed cylinders.
Further according to the present invention, the method includes the step of selecting the agglomerate from the group comprising carbon black, silica, clay, and talc and the polymer is selected from the group comprising elastomer, rubber and thermoplastic.
Also according to the present invention, the method includes the step of breaking up the agglomerates of the compound until at least about 90% of the agglomerates are at a size of less than about 26 microns. Preferably, the agglomerates of the compound are broken up until at least about 95% of the agglomerates are at a size of less than about 26 microns.
Still further according to the present invention, the method includes the step of breaking up the agglomerates of the compound until at least about 90% of the agglomerates are at a size of less than about 10 microns. Preferably, the agglomerates of the compound are broken until at least about 95% of the agglomerates are at a size to a size of less than about 10 microns.
According to the present invention, the method includes the step of disposing a ratio of about 10 parts of polymer to about 1 part of the agglomerates into the one of a pair of opposed pressure cylinders. Preferably, the method includes the step of disposing a ratio of up to 1 part of polymer to about 1 part of the agglomerates into the one of a pair of opposed pressure cylinders.
Also according to the present invention, an apparatus for mixing a mixture of a polymer with an agglomerates of one or more compounds is disclosed that comprises a pair of pressure chambers that are separated from each other by a nozzle block having a nozzle orifice, a piston reciprocally disposed in each of the pressure chambers to force the mixture from one of the pressure chambers through the nozzle orifice and into the other pressure chamber; each of the pistons having a forward surface with an outer portion of the surface disposed at an angle C of between about 0.5 degrees and about 40 degrees with respect to a line perpendicular line to a centerline extending through the pistons; the nozzle orifice having a material flow surface that extends on either side of the nozzle block from the orifice, the material flow surfaces extending at an angle A between about 0.5 degrees and about 40 degrees with respect to a line perpendicular line to a centerline extending through the pair of pressure chambers whereby the material flow surfaces abut against an entrance surface of the orifice.
Further according to the present invention, the nozzle orifice has an entrance surfaces between the material flow surfaces and through slots forming the orifice extending between the pressure chambers, wherein entrance surfaces form an angle B with respect to centerline, where angle B is between about 15 degrees and about 60 degrees.
Also according to the present invention, the outer portion of the surface of forward surfaces have a central protuberance shaped as a truncated cone with a flat outer face and a conically shaped wall that is disposed at an angle D between about 15 degrees and about 60 degrees.
Other objects, features and advantages of the invention will become apparent in light of the following description thereof.